cxgb3i: convert cdev->l2opt to use rcu to prevent NULL dereference

commit e48f129c2f200dde8899f6ea5c6e7173674fc482 upstream.

This oops was reported recently:
d:mon> e
cpu 0xd: Vector: 300 (Data Access) at [c0000000fd4c7120]
    pc: d00000000076f194: .t3_l2t_get+0x44/0x524 [cxgb3]
    lr: d000000000b02108: .init_act_open+0x150/0x3d4 [cxgb3i]
    sp: c0000000fd4c73a0
   msr: 8000000000009032
   dar: 0
 dsisr: 40000000
  current = 0xc0000000fd640d40
  paca    = 0xc00000000054ff80
    pid   = 5085, comm = iscsid
d:mon> t
[c0000000fd4c7450] d000000000b02108 .init_act_open+0x150/0x3d4 [cxgb3i]
[c0000000fd4c7500] d000000000e45378 .cxgbi_ep_connect+0x784/0x8e8 [libcxgbi]
[c0000000fd4c7650] d000000000db33f0 .iscsi_if_rx+0x71c/0xb18
[scsi_transport_iscsi2]
[c0000000fd4c7740] c000000000370c9c .netlink_data_ready+0x40/0xa4
[c0000000fd4c77c0] c00000000036f010 .netlink_sendskb+0x4c/0x9c
[c0000000fd4c7850] c000000000370c18 .netlink_sendmsg+0x358/0x39c
[c0000000fd4c7950] c00000000033be24 .sock_sendmsg+0x114/0x1b8
[c0000000fd4c7b50] c00000000033d208 .sys_sendmsg+0x218/0x2ac
[c0000000fd4c7d70] c00000000033f55c .sys_socketcall+0x228/0x27c
[c0000000fd4c7e30] c0000000000086a4 syscall_exit+0x0/0x40

3 files changed, 42 insertions, 12 deletions

diff --git a/drivers/net/cxgb3/cxgb3_offload.c b/drivers/net/cxgb3/cxgb3_offload.c
index 862804f32b6..3f2e12c3ac1 100644
--- a/drivers/net/cxgb3/cxgb3_offload.c
+++ b/drivers/net/cxgb3/cxgb3_offload.c
@@ -1149,12 +1149,14 @@ static void cxgb_redirect(struct dst_entry *old, struct dst_entry *new)
 		if (te && te->ctx && te->client && te->client->redirect) {
 			update_tcb = te->client->redirect(te->ctx, old, new, e);
 			if (update_tcb) {
+				rcu_read_lock();
 				l2t_hold(L2DATA(tdev), e);
+				rcu_read_unlock();
 				set_l2t_ix(tdev, tid, e);
 			}
 		}
 	}
-	l2t_release(L2DATA(tdev), e);
+	l2t_release(tdev, e);
 }
 
 /*
@@ -1267,7 +1269,7 @@ int cxgb3_offload_activate(struct adapter *adapter)
 		goto out_free;
 
 	err = -ENOMEM;
-	L2DATA(dev) = t3_init_l2t(l2t_capacity);
+	RCU_INIT_POINTER(dev->l2opt, t3_init_l2t(l2t_capacity));
 	if (!L2DATA(dev))
 		goto out_free;
 
@@ -1301,16 +1303,24 @@ int cxgb3_offload_activate(struct adapter *adapter)
 
 out_free_l2t:
 	t3_free_l2t(L2DATA(dev));
-	L2DATA(dev) = NULL;
+	rcu_assign_pointer(dev->l2opt, NULL);
 out_free:
 	kfree(t);
 	return err;
 }
 
+static void clean_l2_data(struct rcu_head *head)
+{
+	struct l2t_data *d = container_of(head, struct l2t_data, rcu_head);
+	t3_free_l2t(d);
+}
+
+
 void cxgb3_offload_deactivate(struct adapter *adapter)
 {
 	struct t3cdev *tdev = &adapter->tdev;
 	struct t3c_data *t = T3C_DATA(tdev);
+	struct l2t_data *d;
 
 	remove_adapter(adapter);
 	if (list_empty(&adapter_list))
@@ -1318,8 +1328,11 @@ void cxgb3_offload_deactivate(struct adapter *adapter)
 
 	free_tid_maps(&t->tid_maps);
 	T3C_DATA(tdev) = NULL;
-	t3_free_l2t(L2DATA(tdev));
-	L2DATA(tdev) = NULL;
+	rcu_read_lock();
+	d = L2DATA(tdev);
+	rcu_read_unlock();
+	rcu_assign_pointer(tdev->l2opt, NULL);
+	call_rcu(&d->rcu_head, clean_l2_data);
 	if (t->nofail_skb)
 		kfree_skb(t->nofail_skb);
 	kfree(t);
diff --git a/drivers/net/cxgb3/l2t.c b/drivers/net/cxgb3/l2t.c
index f452c400325..41540978a17 100644
--- a/drivers/net/cxgb3/l2t.c
+++ b/drivers/net/cxgb3/l2t.c
@@ -300,14 +300,21 @@ static inline void reuse_entry(struct l2t_entry *e, struct neighbour *neigh)
 struct l2t_entry *t3_l2t_get(struct t3cdev *cdev, struct neighbour *neigh,
 			     struct net_device *dev)
 {
-	struct l2t_entry *e;
-	struct l2t_data *d = L2DATA(cdev);
+	struct l2t_entry *e = NULL;
+	struct l2t_data *d;
+	int hash;
 	u32 addr = *(u32 *) neigh->primary_key;
 	int ifidx = neigh->dev->ifindex;
-	int hash = arp_hash(addr, ifidx, d);
 	struct port_info *p = netdev_priv(dev);
 	int smt_idx = p->port_id;
 
+	rcu_read_lock();
+	d = L2DATA(cdev);
+	if (!d)
+		goto done_rcu;
+
+	hash = arp_hash(addr, ifidx, d);
+
 	write_lock_bh(&d->lock);
 	for (e = d->l2tab[hash].first; e; e = e->next)
 		if (e->addr == addr && e->ifindex == ifidx &&
@@ -338,6 +345,8 @@ struct l2t_entry *t3_l2t_get(struct t3cdev *cdev, struct neighbour *neigh,
 	}
 done:
 	write_unlock_bh(&d->lock);
+done_rcu:
+	rcu_read_unlock();
 	return e;
 }
 
diff --git a/drivers/net/cxgb3/l2t.h b/drivers/net/cxgb3/l2t.h
index fd3eb07e3f4..c4dd06689ee 100644
--- a/drivers/net/cxgb3/l2t.h
+++ b/drivers/net/cxgb3/l2t.h
@@ -76,6 +76,7 @@ struct l2t_data {
 	atomic_t nfree;		/* number of free entries */
 	rwlock_t lock;
 	struct l2t_entry l2tab[0];
+	struct rcu_head rcu_head;	/* to handle rcu cleanup */
 };
 
 typedef void (*arp_failure_handler_func)(struct t3cdev * dev,
@@ -99,7 +100,7 @@ static inline void set_arp_failure_handler(struct sk_buff *skb,
 /*
  * Getting to the L2 data from an offload device.
  */
-#define L2DATA(dev) ((dev)->l2opt)
+#define L2DATA(cdev) (rcu_dereference((cdev)->l2opt))
 
 #define W_TCB_L2T_IX    0
 #define S_TCB_L2T_IX    7
@@ -126,15 +127,22 @@ static inline int l2t_send(struct t3cdev *dev, struct sk_buff *skb,
 	return t3_l2t_send_slow(dev, skb, e);
 }
 
-static inline void l2t_release(struct l2t_data *d, struct l2t_entry *e)
+static inline void l2t_release(struct t3cdev *t, struct l2t_entry *e)
 {
-	if (atomic_dec_and_test(&e->refcnt))
+	struct l2t_data *d;
+
+	rcu_read_lock();
+	d = L2DATA(t);
+
+	if (atomic_dec_and_test(&e->refcnt) && d)
 		t3_l2e_free(d, e);
+
+	rcu_read_unlock();
 }
 
 static inline void l2t_hold(struct l2t_data *d, struct l2t_entry *e)
 {
-	if (atomic_add_return(1, &e->refcnt) == 1)	/* 0 -> 1 transition */
+	if (d && atomic_add_return(1, &e->refcnt) == 1)	/* 0 -> 1 transition */
 		atomic_dec(&d->nfree);
 }